1. Field of the Invention
The present invention relates to a resin composition for use in a liquid sealant and a liquid sealant using the resin composition. More particularly, the present invention relates to a resin composition for use in a liquid sealant, which is liquid and has moisture resistance and soldering heat resistance, as well as to a liquid sealant using the resin composition.
2. Description of Related Art
To electronic parts such as those obtained by mounting a semiconductor chip on a metal plate (which is a lead frame) and connecting them electrically using a bonding wire or the like, sealing has been conducted in order to improve, in particular, their reliability. As the sealant for such sealing, ceramics or thermosetting resins are used. Of these sealants, epoxy resin compositions are in wide use for the good balance between economy and properties.
In the fields of semiconductors and electronic parts, higher density, higher integration and smaller size have been strong requirements in recent years. To respond to such requirements, the lead frames or metal wires used in semiconductors or electronic parts are being made increasingly thinner and the circuit patterns used as well in semiconductors and electronic parts are being made increasingly finer.
In the fields of semiconductors and electronic parts, change is being seen also in the method for mounting a sealed electronic part on an electronic circuit, in keeping pace with the above-mentioned higher density and higher integration. As an example, in bonding an electronic part to a substrate with solder, a reflow soldering method (wherein the whole portion of an electronic part is heated) has come to be adopted.
When a substrate such as semiconductor chip of higher density, higher integration or smaller size is sealed according to a conventional transfer molding method, the substrate receives a high pressure during molding; as a result, the substrate easily gives rise to circuit disconnection or poor contact due to displacement of electrode and there has arisen a new problem of reduced yield due to the generation of defects.
In order to solve the above problem of the transfer molding method caused by the high pressure during molding, it is easily conceived of, for example, a new molding method of using a liquid resin (e.g. a liquid epoxy resin) so that substantially no pressure is applied to a substrate during molding. No liquid resin usable in such a molding method, however, has been provided.
Epoxy resin compositions for sealing, used in the conventional transfer molding method, generally have a high viscosity and are substantially unsuitable for use in the above-mentioned new molding method wherein a substrate receives substantially no molding pressure. Moreover, with these epoxy resin compositions, there have been cases that when they are used in mounting by reflow soldering method, the absorbed moisture present in epoxy resin receives thermal shock during mounting and generates peeling or cracking in cured resin; therefore, the epoxy resin compositions have a problem in reliability.
In the conventional transfer molding method, it was proposed as a measure for the above-mentioned reliability problem to (1) increase the amount of inorganic material used in epoxy resin composition for sealing, to reduce the proportion of epoxy resin (this resin is a moisture-absorbing source) or (2) use an epoxy resin of biphenyl type or dicyclopentadiene type skeleton which has a low moisture absorption and which is solid at ordinary temperature.
The epoxy resin compositions for sealing wherein the above measure is used, however, inevitably have a high viscosity. It is therefore apparent that they are unusable in the above-mentioned molding method wherein a substrate receives substantially no molding pressure.